Organic light emitting diode display

ABSTRACT

An organic light emitting diode (OLED) display includes a scan line, a data line, a driving voltage line, a switching transistor, a driving transistor and an OLED. The scan line is formed on a substrate to transmit a scan signal. The data line and the driving voltage line, intersecting the scan line, transmit a data signal and a driving voltage, respectively. The switching transistor, electrically coupled to the scan line and the data line, includes a switching semiconductor layer, a switching gate electrode, and a gate insulating layer having a first thickness. The driving transistor, electrically coupled to the switching drain electrode, includes a driving semiconductor layer, a driving gate electrode and a gate insulating layer having a second thickness. The OLED is electrically coupled to the driving drain electrode. The data line and the driving voltage line are formed with different layers from each other.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. 119 to Korean PatentApplication No. 10-2013-0082152, filed on Jul. 12, 2013 in the KoreanIntellectual Property Office, the disclosure of which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

The present invention relates to an organic light emitting diode (OLED)display.

DISCUSSION OF RELATED ART

Organic light emitting diode (OLED) displays include pixels emittinglight using self-emissive organic emission layers. Holes and electronsinjected to organic emission layers are combined to generate excitons.Such excitions emit light when discharging energy. As the resolution ofthe organic light emitting diode (OLED) display increases, the size ofeach pixel is decreased.

SUMMARY

According to an exemplary embodiment of the present invention, anorganic light emitting diode (OLED) display includes a scan line, a dataline, a driving voltage line, a switching transistor, a drivingtransistor and an OLED. The scan line is formed on a substrate totransmit a scan signal. The data line and the driving voltage lineintersect the scan line and are configured to transmit a data signal anda driving voltage, respectively. The switching transistor iselectrically coupled to the scan line and the data line. The switchingtransistor includes a switching semiconductor layer, a switching gateelectrode, and a gate insulating layer having a first thickness. Thedriving transistor is electrically coupled to the switching drainelectrode of the switching transistor. The driving transistor includes adriving semiconductor layer, a driving gate electrode and a gateinsulating layer having a second thickness. The organic light emittingdiode (OLED) is electrically coupled to the driving drain electrode ofthe driving transistor. The data line and the driving voltage line areformed with different layers from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the present invention will become moreapparent by describing in detail exemplary embodiments thereof withreference to the accompanying drawings of which:

FIG. 1 is a circuit diagram illustrating a pixel of an organic lightemitting diode display according to an exemplary embodiment of thepresent invention;

FIG. 2 is a layout illustrating a pixel according to an exemplaryembodiment of the present invention;

FIG. 3 is a layout illustrating a pixel according to an exemplaryembodiment of the present invention;

FIG. 4 is a cross-sectional view taken along line IV-IV of the organiclight emitting diode display of FIG. 3; and

FIG. 5 is a cross-sectional view taken along lines V-V′ and V′-V″ of theorganic light emitting diode display of FIG. 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described belowin detail with reference to the accompanying drawings. However, thepresent invention may be embodied in different forms and should not beconstrued as limited to the embodiments set forth herein. In thedrawings, the thickness of layers and regions may be exaggerated forclarity. It will also be understood that when an element is referred toas being “on” another element or substrate, it may be directly on theother element or substrate, or intervening layers may also be present.It will also be understood that when an element is referred to as being“coupled to” or “connected to” another element, it may be directlycoupled to or connected to the other element, or intervening elementsmay also be present. Like reference numerals may refer to the likeelements throughout the specification and drawings.

Hereinafter, an organic light emitting diode display according to anexemplary embodiment of the present invention will be described indetail with reference to FIG. 1 to FIG. 5.

FIG. 1 is a circuit diagram of a pixel of an organic light emittingdiode display according to an exemplary embodiment of the presentinvention.

Referring to FIG. 1, a pixel 1 includes a plurality of signal lines 121,122, 123, 124, 171, and 172, and a plurality of transistors T1, T2, T3,T4, T5, and T6, a storage capacitor Cst, and an organic light emittingdiode (OLED).

Hereinafter, the transistor T1 may be referred to as a drivingtransistor (driving thin film transistor) T1. The transistor T2 may bereferred to as a switching transistor (switching thin film transistor)T2. The transistor T3 may be referred to as a compensation transistorT3. The transistor T4 may be referred to as an initialization transistorT4. The transistor T5 may be referred to as an operation controltransistor T5. The transistor T6 may be referred to as a light emissioncontrol transistor T6.

The signal line 121 may be referred to as a scan line 121 fortransferring a scan signal Sn. The signal line 122 may be referred to asa prior scan line 122 for transferring a prior scan signal Sn−1 to theinitialization transistor T4. The signal line 123 may be referred to asa light emission control line 123 for transferring a light emissioncontrol signal En to the operation control transistor T5 and the lightemission control transistor T6. The signal line 171 may be referred toas a data line 171 for transferring a data signal Dm. The signal line172 may be referred to as a driving voltage line 172 for transferring adriving voltage ELVDD. The signal line 124 may be referred to as aninitialization voltage line 124 for transferring an initializationvoltage Vint. The initialization voltage Vint serves to initialize thedriving transistor T1.

A gate electrode G1 of the driving transistor T1 is connected to a firstelectrode Cst1 of the storage capacitor Cst, a source electrode S1 ofthe driving transistor T1 is connected via the operation controltransistor T5 to the driving voltage line 172, and the drain electrodeD1 of the driving transistor T1 is electrically connected via the lightemission control transistor T6 to an anode of the organic light emittingdiode (OLED). The driving transistor T1 receives the data signal Dmaccording to a switching operation of the switching transistor T2 tosupply a driving current Id to the organic light emitting diode (OLED).

A gate electrode G2 of the switching transistor T2 is connected to thescan line 121, a source electrode S2 of the switching transistor T2 isconnected to the data line 171, and a drain electrode D2 of theswitching transistor T2 is connected to the source electrode S1 of thedriving transistor T1 and connected via the operation control transistorT5 to the driving voltage line 172. The switching transistor T2 servesto transfer the data signal Dm, according to the scan signal Sn, to thesource electrode of the driving transistor T1.

A gate electrode G3 of the compensation transistor T3 is connected tothe scan line 121, a source electrode S3 of the compensation transistorT3 is connected to the drain electrode D1 of the driving transistor T1and connected via the light emission control transistor T6 to the anodeof the organic light emitting diode (OLED), and a drain electrode D3 ofthe compensation transistor T3 is connected to the first electrode Cst1of the storage capacitor Cst, a drain electrode D4 of the initializationtransistor T4, and the gate electrode G1 of the driving transistor T1.The compensation transistor T3 is turned on according to the scan signalSn transferred through the scan line 121 to connect the gate electrodeG1 and the drain electrode D1 of the driving transistor T1 to eachother, thus rendering the driving transistor T1 to performing as adiode.

A gate electrode G4 of the initialization transistor T4 is connected tothe prior scan line 122, the source electrode S4 of the initializationtransistor T4 is connected to the initialization voltage line 124, andthe drain electrode D4 of the initialization transistor T4 is connectedto the first electrode Cst1 of the storage capacitor Cst, the drainelectrode D3 of the compensation transistor T3, and the gate electrodeG1 of the driving transistor T1. The initialization transistor T4 isturned on according to the prior scan signal Sn−1 transferred throughthe prior scan line 122 to transfer the initialization voltage Vint tothe gate electrode G1 of the driving transistor T1, thus initializingthe voltage of the gate electrode G1 of the driving transistor T1 to theinitialization voltage Vint.

A gate electrode G5 of the operation control transistor T5 is connectedto the light emission control line 123, a source electrode S5 of theoperation control transistor T5 is connected to the driving voltage line172, and a drain electrode D5 of the operation control transistor T5 isconnected to the source electrode S1 of the driving transistor T1 andthe drain electrode D2 of the switching transistor T2.

A gate electrode G6 of the light emission control transistor T6 isconnected to the light emission control line 123, a source electrode S6of the light emission control transistor T6 is connected to the drainelectrode D1 of the driving transistor T1 and the source electrode S3 ofthe compensation transistor T3, and a drain electrode D6 of the lightemission control transistor T6 is electrically connected to the anode ofthe organic light emitting diode (OLED). The operation controltransistor T5 and the light emission control transistor T6 aresimultaneously turned on according to the light emission control signalEn transferred through the light emission control line 123 to transferthe driving voltage ELVDD to the organic light emitting diode (OLED),thus allowing the driving current Id to flow through the organic lightemitting diode (OLED).

A second electrode Cst2 of the storage capacitor Cst is connected to thedriving voltage line 172, and a cathode of the organic light emittingdiode (OLED) is connected to a common voltage ELVSS. Accordingly, theorganic light emitting diode (OLED) receives the driving current Id fromthe driving transistor T1 to emit light, thereby displaying an image.

Hereinafter, an operation of a pixel of an organic light emitting diodedisplay according to an exemplary embodiment of the present inventionwill be described in detail.

First, the prior scan signal Sn−1 at a low level is supplied through theprior scan line 122 during an initialization period. Then, theinitialization transistor T4 is turned on in response to the prior scansignal Sn−1 at the low level, and the initialization voltage Vint isconnected from the initialization voltage line 124 through theinitialization transistor T4 to the gate electrode of the drivingtransistor T1 to initialize the driving transistor T1 using theinitialization voltage Vint.

Subsequently, the scan signal Sn at the low level is supplied throughthe scan line 121 during a data programming period. Then, the switchingtransistor T2 and the compensation transistor T3 are turned on inresponse to the scan signal Sn at the low level.

In this case, the driving transistor T1 is diode-connected by theturned-on compensation transistor T3, and is biased in a forwarddirection.

Then, a compensation voltage Dm+Vth is applied to the gate electrode ofthe driving transistor T1 to prevent a threshold voltage drop across thedriving transistor T1. The Vth is a threshold voltage of the drivingtransistor T1 and has a negative voltage.

The driving voltage ELVDD and the compensation voltage Dm+Vth areapplied to respective electrodes of the storage capacitor Cst, and acharge corresponding to a voltage difference between the respectiveelectrodes is stored in the storage capacitor Cst. Thereafter, the levelof the light emission control signal En supplied from the light emissioncontrol line 123 during the light emission period is changed from thehigh level to the low level. Then, the operation control transistor T5and the light emission control transistor T6 are turned on by the lightemission control signal En at the low level during the light emissionperiod.

Subsequently, the driving current Id supplied to the organic lightemitting diode (OLED) corresponds to a voltage difference between thegate electrode of the driving transistor T1 and the driving voltageELVDD. A gate-source voltage Vgs of the driving transistor T1 ismaintained at “(Dm+Vth)−ELVDD” using the storage capacitor Cst duringthe light emission period. The driving current Id is proportional to asquare of a difference between the threshold voltage and the source-gatevoltage of the driving transistor T1, that is, “(Dm−ELVDD)²”, accordingto a current-voltage relationship of the driving transistor T1.Accordingly, the driving current Id is determined regardless of thethreshold voltage Vth of the driving transistor T1.

Now, a detailed structure of the pixel of the organic light emittingdiode display illustrated in FIG. 1 will be described in detail withreference to FIGS. 2 to 5 together with FIG. 1.

FIGS. 2 and 3 are layouts illustrating a pixel according to an exemplaryembodiment of the present invention, FIG. 4 is a cross-sectional view,taken along line IV-IV, of the organic light emitting diode display ofFIG. 3, which is, and FIG. 5 is a cross-sectional view, taken alonglines V-V′ and V′-V″, of the organic light emitting diode display ofFIG. 3.

Referring to FIG. 2, an organic light emitting diode display accordingto an exemplary embodiment of the present invention includes a scan line121, a prior scan line 122, a light emission control line 123, and aninitialization voltage line 124 applying a scan signal Sn, a prior scansignal Sn−1, a light emission control signal En, and an initializationvoltage Vint, respectively. The signal lines 121, 122, 123 and 124 areextended in a row direction. A data line 171 and a driving voltage line172 cross the signal lines 121 to 124. The data line 171 and the drivingvoltage line 172 apply a data signal Dm and a driving voltage ELVDD,respectively, to the pixel.

Further, the driving transistor T1, the switching transistor T2, thecompensation transistor T3, the initialization transistor T4, theoperation control transistor T5, the light emission control transistorT6, the storage capacitor Cst, and the organic light emitting diode(OLED) are formed in the pixel.

The driving transistor T1, the switching transistor T2, the compensationtransistor T3, the initialization transistor T4, the operation controltransistor T5, and the light emission control transistor T6 are formedalong a semiconductor layer 131. The semiconductor layer 131 is formedto be bent in various shapes. The semiconductor layer 131 may be formedof polysilicon or an oxide semiconductor. The oxide semiconductor mayinclude oxides having titanium (Ti), hafnium (Hf), zirconium (Zr),aluminum (Al), tantalum (Ta), germanium (Ge), zinc (Zn), gallium (Ga),tin (Sn), indium (In), or a mixture thereof. For example, the oxidesemiconductor may include, but is not limited to, zinc oxide (ZnO),indium-gallium-zinc oxide (InGaZnO4), indium-zinc oxide (Zn—In—O),zinc-tin oxide (Zn—Sn—O) indium-gallium oxide (In—Ga—O), indium-tinoxide (In—Sn—O), indium-zirconium oxide (In—Zr—O), indium-zirconium-zincoxide (In—Zr—Zn—O), indium-zirconium-tin oxide (In—Zr—Sn—O),indium-zirconium-gallium oxide (In—Zr—Ga—O), indium-aluminum oxide(In—Al—O), indium-zinc-aluminum oxide (In—Zn—Al—O), indium-tin-aluminumoxide (In—Sn—Al—O), indium-aluminum-gallium oxide (In—Al—Ga—O),indium-tantalum oxide (In—Ta—O), indium-tantalum-zinc oxide(In—Ta—Zn—O), indium-tantalum-tin oxide (In—Ta—Sn—O),indium-tantalum-gallium oxide (In—Ta—Ga—O), indium-germanium oxide(In—Ge—O), indium-germanium-zinc oxide (In—Ge—Zn—O),indium-germanium-tin oxide (In—Ge—Sn—O), indium-germanium-gallium oxide(In—Ge—Ga—O), titanium-indium-zinc oxide (Ti—In—Zn—O), orhafnium-indium-zinc oxide (Hf—In—Zn—O). In the case where thesemiconductor layer 131 is formed of an oxide semiconductor, aprotective layer may be formed on the semiconductor layer 131 to protectthe oxide semiconductor that is weak to an external environment such ashigh temperatures.

The semiconductor layer 131 includes a channel region that is subject tochannel doping with an N-type impurity or a P-type impurity, and asource region and a drain region that are formed at respective sides ofthe channel region and formed by doping a doping impurity having a typethat is opposite to that of the doping impurity doped in the channelregion.

Hereinafter, a layout of an organic light emitting diode displayaccording to an exemplary embodiment of the present invention will bedescribed in detail with reference to FIGS. 2 and 3, and across-sectional structure thereof will be described in detail withreference to FIGS. 4 and 5.

First, referring to FIGS. 2 and 3, a pixel of an organic light emittingdiode display according to an exemplary embodiment of the presentinvention includes the driving transistor T1, the switching transistorT2, the compensation transistor T3, the initialization transistor T4,the operation control transistor T5, the light emission controltransistor T6, the storage capacitor Cst, and the organic light emittingdiode (OLED). The transistors T1, T2, T3, T4, T5, and T6 are formedalong the semiconductor layer 131. The semiconductor layer 131 includesa driving semiconductor layer 131 a formed in the driving transistor T1,a switching semiconductor layer 131 b formed in the switching transistorT2, a compensation semiconductor layer 131 c formed in the compensationtransistor T3, an initialization semiconductor layer 131 d formed in theinitialization transistor T4, an operation control semiconductor layer131 e formed in the operation control transistor T5, and a lightemission control semiconductor layer 131 f formed in the light emissioncontrol transistor T6.

The driving transistor T1 includes the driving semiconductor layer 131a, a driving gate electrode 125 a, a driving source electrode 176 a, anda driving drain electrode 177 a. The driving semiconductor layer 131 aincludes a driving channel region overlapped with the driving gateelectrode 125 a. The driving semiconductor layer 131 a also includes adriving source region 176 a corresponding to the driving sourceelectrode 176 a and a driving drain region 177 a corresponding to thedriving drain electrode 177 a. The driving source region 176 a is formedat one side of the channel region of the driving semiconductor layer 131a. The driving source region 176 a is doped with impurities in thedriving semiconductor layer 131 a. The driving drain region 177 a isformed at the other side of the channel region of the drivingsemiconductor layer 131 a. The driving drain region 177 a is doped withimpurities in the driving semiconductor layer 131 a. The driving gateelectrode 125 a is formed with substantially the same material as thatof the data line 171 and a connection member 174. For example, thedriving gate electrode 125 a, the data line 171, and the connectionmember 174 may be simultaneously formed using substantially the samematerial.

The switching transistor T2 includes the switching semiconductor layer131 b, a switching gate electrode 125 b, a switching source electrode176 b, and a switching drain electrode 177 b. The switchingsemiconductor layer 131 b includes a switching channel region overlappedwith the switching gate electrode 125 b. The switching semiconductorlayer 131 b also includes a switching source region corresponding to theswitching source electrode 176 b and a switching drain regioncorresponding to the switching drain electrode 177 b. The switchingsource electrode 176 b is connected to the data line 171 through acontact hole 69. The switching drain region 177 b is doped with impurityin the switching semiconductor layer 131 b.

The switching gate electrode 125 b is formed with substantially the samematerial as the scan line 121, the prior scan line 122, the lightemission control line 123, the initialization voltage line 124, acompensation gate electrode 125 c, an initialization gate electrode 125d, an operation control gate electrode 125 e, a light emission controlgate electrode 125 f, and a second storage capacitive plate 127. Forexample, the switching gate electrode 125 b, the scan line 121, theprior scan line 122, the light emission control line 123, theinitialization voltage line 124, a compensation gate electrode 125 c, aninitialization gate electrode 125 d, an operation control gate electrode125 e, a light emission control gate electrode 125 f, and a secondstorage capacitive plate 127 may be simultaneously formed usingsubstantially the same material.

The compensation transistor T3 includes the compensation semiconductorlayer 131 c, the compensation gate electrode 125 c, a compensationsource electrode 176 c, and a compensation drain electrode 177 c. Thecompensation semiconductor layer 131 c includes a compensation channelregion overlapped with the compensation gate electrode 125 c. Thecompensation semiconductor layer 131 c also includes a compensationsource region 176 c corresponding to the compensation source electrode176 c and a compensation drain region corresponding to the compensationdrain electrode 177 c. The initialization transistor T4 includes theinitialization semiconductor layer 131 d, the initialization gateelectrode 125 d, an initialization source electrode 176 d, and aninitialization drain electrode 177 d. The initialization semiconductorlayer 131 d includes an initialization channel region overlapped withthe initialization gate electrode 125 d. The initialization gateelectrode 125 d is part of the prior scan line 122. The initializationsemiconductor 131 d also includes an initialization source regioncorresponding to the initialization source electrode 176 d and aninitialization drain region corresponding to the initialization drainelectrode 177 d. The initialization source electrode 176 d is connectedthrough a contact hole 61 to the initialization source region that isformed at one side of the initialization gate electrode 125 d. Theinitialization drain electrode 177 d is connected through a contact hole63 to the initialization drain region that is formed at the other sideof the initialization gate electrode 125 d.

The operation control transistor T5 includes the operation controlsemiconductor layer 131 e, the operation control gate electrode 125 e,an operation control source electrode 176 e, and an operation controldrain electrode 177 e. The operation control semiconductor layer 131 eincludes an operation control channel region overlapped with theoperation control source electrode 176 e. The operation control sourceelectrode 176 e is part of the driving voltage line 172 and is connectedto an operation control source region 132 e through a contact hole 71.The operation control drain electrode 177 e corresponds to an operationcontrol drain region 177 e doped with impurities in the operationcontrol semiconductor layer 131 e.

The light emission control transistor T6 includes the light emissioncontrol semiconductor layer 131 f, the light emission control gateelectrode 125 f, a light emission control source electrode 176 f, and alight emission control drain electrode 177 f. The light emission controlsemiconductor layer 131 f includes a light emission control channelregion overlapped with the light emission control gate electrode 125 f.The light emission control gate electrode 125 is part of the lightemission control line 123. The light emission control semiconductorlayer 131 f also includes a light emission control source regioncorresponding to the light emission control source electrode 176 f and alight emission control drain region corresponding to the light emissioncontrol drain electrode 177 f. The light emission control source region176 f is doped with impurities in the light emission controlsemiconductor layer 131 f.

An end of the driving semiconductor layer 131 a of the drivingtransistor T1 is connected to the switching semiconductor layer 131 band the operation control semiconductor layer 131 e, and another end ofthe driving semiconductor layer 131 a is connected to the compensationsemiconductor layer 131 c and the light emission control semiconductorlayer 131 f. Therefore, the driving source electrode 176 a is connectedto the switching drain electrode 177 b and the operation control drainelectrode 177 e, and the driving drain electrode 177 a is connected tothe compensation source electrode 176 c and the light emission controlsource electrode 176 f.

The storage capacitor Cst includes a first storage capacitive plate 126,the second storage capacitive plate 127, and a dielectric oxide layerinterposed therebetween. For example, the dielectric oxide layer maycorrespond to a first gate insulating layer 141 of FIGS. 4 and 5, whichwill be described later. The first storage capacitive plate 126 isformed with substantially the same material as the semiconductor layer131. For example, the first storage capacitive plate 126 and thesemiconductor layer 131 may be simultaneously formed. The second storagecapacitive plate 127 is formed with substantially the same material asthe scan line 121, the prior scan line 122, the light emission controlline 123, the initialization voltage line 124, the switching gateelectrode 125 b, the compensation gate electrode 125 c, theinitialization gate electrode 125 d, the operation control gateelectrode 125 e, and the light emission control gate electrode 125 f.For example, the second storage capacitive plate 127, the scan line 121,the prior scan line 122, the light emission control line 123, theinitialization voltage line 124, the switching gate electrode 125 b, thecompensation gate electrode 125 c, the initialization gate electrode 125d, the operation control gate electrode 125 e, and the light emissioncontrol gate electrode 125 f may be simultaneously formed.

Herein, a storage capacitance is determined by charges accumulated inthe storage capacitor Cst and a voltage between both capacitive plates126 and 127.

The driving voltage line 172 overlapping and passing the storagecapacitor Cst overlaps and passes the scan line 121, the prior scan line122, the light emission control line 123, and the initialization voltageline 124. A portion of the driving voltage line 172 corresponds to theoperation control source electrode 176 e and is connected to theoperation control source region 132 e through the contact hole 71, andanother portion of the driving voltage line 172 is connected to thesecond storage capacitive plate 127 through a contact hole 66. Thecontact hole 66 may be formed in the interlayer insulating layer 160 andthe second gate insulating layer 142, which will be described later withreference to FIGS. 4 and 5.

The connection member 174 parallel to the driving voltage line 172 isformed with substantially the same layer as the data line 171. Theconnection member 174 connects the driving gate electrode 125 a and thefirstd storage capacitive plate 126 to each other. A sub connectionmember 178 is formed with substantially the same layer as the drivingvoltage line 172. The sub connection member 178 is connected through acontact hole 63 to both the firstd storage capacitive plate 126 and theconnection member 174.

Accordingly, the storage capacitor Cst stores a storage capacitancecorresponding to the voltage difference between the driving voltageELVDD transmitted through the driving voltage line 172 and the gatevoltage of the driving gate electrode 125 a.

The switching transistor T2 is used as a switching element selecting apixel to emit light. The switching gate electrode 125 b is connected tothe scan line 121, the switching source electrode 176 b is connected tothe data line 171, and the switching drain electrode 177 b is connectedto the driving transistor T1 and the operation control transistor T5. Inaddition, the light emission control drain electrode 177 f of the lightemission control transistor T6 is directly connected through a contacthole 181 formed in a protective layer 180 to a pixel electrode 191 of anorganic light emitting diode 70. The contact hole 181 and the pixelelectrode 191 will be described later with reference to FIGS. 4 and 5.

Referring to FIG. 4 and FIG. 5, a structure of an organic light emittingdiode (OLED) display according to an exemplary embodiment of the presentinvention will be described.

A vertical structure of the transistors T1, T2 and T6 of FIG. 3 will bedescribed. A vertical structure of the compensation transistor T3 andthe initialization transistor T4 may have substantially the same as thatof the switching transistor T2, and a vertical structure of theoperation control transistor T5 may have substantially the same as thatof the light emission control transistor T6.

A buffer layer 120 is formed on a substrate 110. The substrate 110 maybe formed of an insulating substrate including, but is not limited to,glass, quartz, ceramics, plastics, or the like.

The driving semiconductor layer 131 a, the switching semiconductor layer131 b, the light emission control semiconductor layer 131 f, and thefirst storage capacitive plate 126 are formed on the buffer layer 120.The driving semiconductor layer 131 a includes a driving channel region131 a 1, the driving source region 176 a and the driving drain region177 a. The driving channel region 131 a 1 is interposed between thedriving source region 176 a and the driving drain region 177 a. Theswitching semiconductor layer 131 b includes a switching channel region131 b 1, the switching source region 132 b, and the switching drainregion 177 b. The switching channel region 131 b 1 is interposed betweenthe switching source region 132 b and the switching drain region 177 b.The light emission control transistor T6 includes a light emissioncontrol channel region 131 f 1, the light emission control source region176 f, and a light emission control drain region 133 f. The lightemission control channel region 131 f 1 is interposed between the lightemission control source region 176 f and a light emission control drainregion 133 f.

The first gate insulating layer 141 is formed on the switchingsemiconductor layer 131 a, the driving semiconductor layer 131 b, andthe light emission control semiconductor layer 131 f. The first gateinsulating layer 141 is formed of a high dielectric constant materialincluding, but is not limited to, HfOx, ZrOx, AlOx, or SiOx.

The first gate wires 121, 122, 123, 124, 125 b, 125 f, and 127 includingthe scan line 121 including the switching gate electrode 125 b, theprior scan line 122, the light emission control line 123 including thelight emission control gate electrode 125 f, the initialization voltageline 124, and the second storage capacitive plate 127 are formed on thefirst gate insulating layer 141. The signal lines 121, 122, 123, 124,125 b, 125 f, and 127 may be collectively referred to as first gatewires.

The second gate insulating layer 142 is formed on the first gate wires121, 122, 123, 124, 125 b, 125 f, and 127 and the first gate insulatinglayer 141. The second gate insulating layer 142 is formed of siliconnitride (SiNx) or silicon oxide (SiO2).

The driving gate electrode 125 a and the data line 171 are formed on thesecond gate insulating layer 142. The driving gate electrode 125 a andthe data line 171 may be collectively referred to as second gate wires.

As described above, the first gate insulating layer 141 and the secondgate insulating layer 142 are formed between the driving semiconductorlayer 131 a and the driving gate electrode 125 a, and thus the drivingtransistor T1 having a gate insulating layer thicker than othertransistors of the pixel 1. The first gate insulating layer 141 and thesecond gate insulating layer 142 constitutes the gate insulating layerof the driving transistor T1. Accordingly, the gate voltage applied tothe driving gate electrode 125 a is increased to higher voltages,thereby the pixel 1 displaying various grayscales.

The storage capacitance of the storage capacitor Cst may be increasedusing the first gate insulating layer 141 made of a high dielectricconstant material.

Also, by forming the data line 171 with the same layer as the drivinggate electrode 125 a, the data line 171 is formed with a different layerfrom the driving voltage line 172 such that the data line 171 and thedriving voltage line 172 may overlap, thereby implementing a highresolution display.

The interlayer insulating layer 160 is formed on the second gate wires125 a and 171 and the second gate insulating layer 142. The interlayerinsulating layer 160 may be made of a ceramic-based material including,but is not limited to, silicon nitride (SiNx) or silicon oxide (SiO2).

The driving voltage line 172, the switching connection plate 175, andthe light emission control drain electrode 177 f are formed on theinterlayer insulating layer 160. The data wires 172, 175, and 177 f maybe collectively referred to as data wires.

The light emission control drain electrode 177 f is connected through acontact hole 72 formed in the first gate insulating layer 141, thesecond gate insulating layer 142, and the interlayer insulating layer160 to the light emission control drain region 133 f of the lightemission control semiconductor layer 131 f.

The protective layer 180 is formed on the data wires 172, 175, and 177f. The pixel electrode 191 is formed on the protective layer 180. Thepixel electrode 191 is connected to the light emission control drainelectrode 177 f through the contact hole 181 formed in the protectivelayer 180.

A barrier rib 350 is formed on an edge of the pixel electrode 191 andthe protective layer 180, and the barrier rib 350 has a barrier ribopening 351 through which the pixel electrode 191 is exposed. Thebarrier rib 350 may be made of resins including, but is not limited to,polyacrylates and polyimides, or silica-based inorganic materials.

An organic emission layer 370 is formed on the pixel electrode 191exposed through the barrier rib opening 351, and a common electrode 270is formed on the organic emission layer 370. As described above, theorganic light emitting diode 70 including the pixel electrode 191, theorganic emission layer 370, and the common electrode 270 is formed.

Herein, the pixel electrode 191 is an anode that is a hole injectionelectrode, and the common electrode 270 is a cathode that is an electroninjection electrode. However, the pixel electrode 191 may be a cathodeand the common electrode 270 may be an anode according to a drivingmethod of the organic light emitting diode display. Holes and electronsare injected from the pixel electrode 191 and the common electrode 270into the organic emission layer 370, and when excitons that are formedof the injected holes and electrons fall from an exited state to aground state, light is emitted.

The organic emission layer 370 is formed of a low molecular weightorganic material or a high molecular weight organic material such asPEDOT (poly(3,4-ethylenedioxythiophene)). Further, the organic emissionlayer 370 may be formed of a multilayer including one or more of anemission layer, a hole injection layer HIL, a hole transport layer HTL,an electron transport layer ETL, and an electron injection layer EIL.The hole injection layer HIL may be disposed on the pixel electrode 191that is the anode, and the hole transport layer HTL, the emission layer,the electron transport layer ETL, and the electron injection layer EILmay be sequentially laminated thereon.

The organic emission layer 370 may include a red organic emission layeremitting light having a red color, a green organic emission layeremitting light having a green color, and a blue organic emission layeremitting light having a blue color, and the red organic emission layer,the green organic emission layer, and the blue organic emission layerare respectively formed in a red pixel, a green pixel, and a blue pixelto display a color image.

Further, the organic emission layer 370 may display a color image usingthe red organic emission layer, the green organic emission layer, andthe blue organic emission layer disposed in the red pixel, the greenpixel, and the blue pixel respectively. A red color filter, a greencolor filter, and a blue color filter may be disposed for each pixel.Alternatively, a white organic emission layer emitting light having awhite color may be formed in the red pixel, the green pixel, and theblue pixel. A red color filter, a green color filter, and a blue colorfilter may be formed for each pixel to display a color image. For thewhite organic emission layer, separate deposition masks for depositing ared organic emission layer, a green organic emission layer, and a blueorganic emission layer in each pixel including a red pixel, a greenpixel, and a blue pixel need not be used.

Alternatively, a white organic emission layer may be laminated to emit awhite color. For example, the white organic emission layer may includeat least one yellow organic emission layer and at least one blue organicemission layer to emit light having the white color. The white organicemission layer may include at least one cyan organic emission layer andat least one red organic emission layer to emit a white color. The whiteorganic emission layer may include at least one magenta organic emissionlayer and at least one green organic emission layer to emit a whitecolor.

When the common electrode 270 may be formed of a reflective conductivematerial, a rear surface light emission type of organic light emittingdiode display is obtained. The reflective material may include, but isnot limited to, lithium (Li), calcium (Ca), lithium fluoride/calcium(LiF/Ca), lithium fluoride/aluminum (LiF/Al), aluminum (Al), silver(Ag), magnesium (Mg), or gold (Au).

While the present invention has been shown and described with referenceto exemplary embodiments thereof, it will be apparent to those ofordinary skill in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of the presentinvention as defined by the following claims.

What is claimed is:
 1. An organic light emitting diode (OLED) displaycomprising: a substrate; a scan line formed on the substrate andconfigured to transmit a scan signal; a data line and a driving voltageline intersecting the scan line and configured to transmit a data signaland a driving voltage, respectively; a switching transistor electricallycoupled to the scan line and the data line and including a switchingsemiconductor layer, a switching gate electrode, and a gate insulatinglayer having a first thickness; a driving transistor electricallycoupled to the switching drain electrode of the switching transistor andincluding a driving semiconductor layer, a driving gate electrode and agate insulating layer having a second thickness; and an organic lightemitting diode (OLED) electrically coupled to the driving drainelectrode of the driving transistor, wherein the data line and thedriving voltage line are formed with different layers from each other.2. The organic light emitting diode (OLED) display of claim 1, whereinthe driving gate electrode is formed at different layer from theswitching gate electrode.
 3. The organic light emitting diode (OLED)display of claim 2, wherein the driving gate electrode and the data lineare formed at the same layer.
 4. The organic light emitting diode (OLED)display of claim 3, further comprising: a first gate insulating layercovering a semiconductor layer having the switching semiconductor layerand the driving semiconductor layer; and a second gate insulating layerformed on the first gate insulating layer, wherein the switching gateelectrode is interposed between the first gate insulating layer and thesecond gate insulating layer, wherein the driving gate electrode and thedata line are formed on the second gate insulating layer.
 5. The organiclight emitting diode (OLED) display of claim 4, further comprising aninterlayer insulating layer covering the driving gate electrode and thedata line, and the driving voltage line is formed on the interlayerinsulating layer.
 6. The organic light emitting diode (OLED) display ofclaim 5, further comprising: a storage capacitor having a first storagecapacitive plate, wherein the first storage capacitive plate is formedof substantially the same material of the semiconductor layer and thefirst storage capacitive plate is formed with the same layer as thesemiconductor layer; and a second storage capacitive plate formed on thefirst gate insulating layer covering the first storage capacitive plateand overlapping the first storage capacitive plate, wherein the drivingvoltage line is connected to the second storage capacitive plate.
 7. Theorganic light emitting diode (OLED) display of claim 6, wherein thefirst gate insulating layer is formed of a high dielectric constantmaterial.
 8. The organic light emitting diode (OLED) display of claim 7,wherein the high dielectric constant material includes HfOx, ZrOx, AlOx,or SiOx.
 9. The OLED display of claim 1, wherein the second thickness isgreater than the first thickness.
 10. The OLED display of claim 4,wherein the first gate insulating layer constitutes the gate insulatinglayer of the switching transistor, and the first and second gateinsulating layers constitute the gate insulating layer of the drivingtransistor.